Detection of Surface Spins Causing Flux Noise in Quantum Devices Using Electron Spin Resonance

The improvement of quantum computing technologies relies on the reduction of flux noise that contributes to decoherence. Recent work has shown that the majority of flux noise is due to impurities and defects on the surface of the qubits [1], [2]. Electron spin resonance (ESR) is a prime candidate to detect these defects, but lacks the sensitivity and ability to provide information on the physical location of the defects. We report upon ESR measurements utilizing a non-resonant probe integrated within a semiconductor wafer probing station which could be used to detect paramagnetic defects believed to contribute to flux noise in quantum devices. Our approach greatly enhances ESR's sensitivity and provides a high spatial resolution on the surface of unaltered fully processed wafers and devices at room temperature. We demonstrate the effectiveness of our method to detect defects on the surface of materials with a spin sensitivity improvement of roughly 10,000 × compared to classical ESR. The integration of a non-resonant probe into a standard semiconductor wafer probing setup has already been shown to be able to obtain a 2D map of unpaired spins on the surface of samples [3]. The technique offers a pathway for characterization of the defects which contribute to flux noise, which would provide critical insight into reducing decoherence mechanisms.